Conventionally, an oil supply system that supplies engine oil (lubricating oil) to a portion to be lubricated or a portion to be cooled is provided in an engine mounted on an automobile and the like (see Patent Literature 1 and Patent Literature 2). Also, oil jet apparatuses have been known as instruments provided in the oil supply system. The oil jet apparatus injects the engine oil to the rear surface of a piston (hereinafter, the oil injection is referred to as “oil jet”).
The oil jet apparatuses disclosed in Patent Literature 1 and Patent Literature 2 are configured to switch the execution and non-execution of the oil jet. For example, an oil jet switching valve is installed in the oil supply path of the oil jet apparatus. At the initial time of the start-up of the cooling an engine, and the like, the oil jet switching valve is closed, and the oil jet is stopped. In this manner, the improvement of the warm-up performance of the engine is achieved. Additionally, the atomization of fuel injected in cylinders is facilitated, thereby achieving the improvement of exhaust emission or the prevention of oil dilution (dilution of oil caused by the fuel). On the other hand, after the completion of the warm-up of the engine and the like, when engine load increases, the oil jet switching valve is opened, and the oil jet is executed. Accordingly, this cools the pistons, and suppresses the excessive increase in the in-cylinder temperature, thereby preventing the occurrence of knocking.